In recent decades accompanying rapid advances in information-oriented society, there have also been rapid technological advances to provide devices and systems for gathering and communicating information. Of these, display devices have been designed for television screens, commercial signage, personal and laptop computers, personal display devices, and phones of all types, to name the most common information sharing devices.
In display devices where a continuous conductive film is not practical for providing this protection from electromagnetic radiation emission, it has been found that conductive mesh or patterns can be used for electromagnetic wave shielding purpose.
Other technologies have been developed to provide new microfabrication methods to provide metallic, two-dimensional, and three-dimensional structures with conductive metals. Patterns have been provided for these purposes using photolithography and imaging through mask materials.
Improvements have been proposed for providing conductive patterns using photosensitive silver salt compositions such as silver halide emulsions. Such techniques have a number of disadvantages that are described in the art and efforts continue to make additional improvements.
As the noted display devices have developed in recent years, their attraction has increased greatly with the use of touch screen technology whereby a light touch on the screen surface with a finger or stylus can create signals to cause changes in screen views or cause the reception or sending of information, telecommunications, interaction with the internet, and many other features that are being developed at an ever-increasing pace of innovation. The touch screen technology has been made possible largely by the use of transparent conductive grids on the primary display so that the location of the noted touch on the screen surface can be detected by appropriate electrical circuitry and software. For a number of years, touch screen displays have been prepared using indium tin oxide (ITO) coatings to create arrays of capacitive patterns or areas used to distinguish multiple point contacts. ITO can be readily patterned using known semiconductor fabrication methods including photolithography and high vacuum processing. However, the use of ITO coatings has a number of disadvantages. Indium is an expensive rare earth metal and is available in limited supply. Moreover, ITO is a ceramic material and is not easily bent or flexed and such coatings require expensive vacuum deposition methods and equipment. In addition, ITO conductivity is relatively low, requiring short line lengths to achieve desired response rates (upon touch). Touch screens used in large displays are broken up into smaller segments in order to reduce the conductive line length to an acceptable electrical resistance. These smaller segments require additional driving and sensing electronics, further adding to the cost of the devices.
Silver is an ideal conductor having conductivity that is 50 to 100 times greater than that of ITO. Unlike most metal oxides, silver oxide is still reasonably conductive and its use reduces the problem of making reliable electrical connections. Moreover, silver is used in many commercial applications and is available from numerous commercial sources.
In other technologies, transparent polymeric films have been treated with conductive metals such as silver, copper, nickel, and indium by such methods as sputtering, ion plating, ion beam assist, wet coating, as well as the vacuum deposition. However, all of these technologies are expensive, tedious, or extremely complicated so that the relevant industries are spending considerable resources to design improved means for forming conductive patterns for various devices especially touch screen displays.
U.S. Pat. No. 5,925,415 (Fry et al.) describes a method for electroless plating on a substrate surface having hydroxyl groups involving treatment with silyl hydride to form silicon hydroxide bonds, followed by deposition of silver ions, and electroless plating.
U.S. Patent Application Publication 2011/0117338 (Poquette et al.) describes electroless plating of open pore foam materials using tin or palladium catalysts.
U.S. Patent 2005/0133904 (Kim et al.) describes a method for forming multilayer pattern for hermetic sealing of packages by coating a titanate based photocatalytic compound to form a film, UV exposure, growing palladium catalysts, and electrolessly plating a metal.
Yan et al., Chem. Mater. 1995, 7, 2007-2009 describe the preparation of amorphous coatings using a composition of titanium alkoxide, acetoacetate, water, ethanol, propanol, and HCl on a porous silica substrate to provide differences in refractive index.
Tadanaga et al., Chem. Mater. 2000, 12, 590-592 describe the use of titanium alkoxide, acetoacetate, and water in a composition to form a superhydrophobic-superhydrophilic pattern on an alumina layer.
Stathatos et al. Langmuir 2000, 16, 2398-2400 describes photocatalytically depositing silver nanoparticles on mesoporous titanium dioxide films.
Despite the advances in the art to provide conductive metal patterns for various devices, it is very difficult to form very fine (thin) conductive lines on flexible films for electronic devices of all types. Catalytic seed materials must have significant durability to withstand electroless plating conditions and baths. Other problems are experienced with various known patterning materials and there remains a need to provide high strength, thin conductive lines.